Liposomes have been used in targeted drug delivery and recently in the development of oral vaccines using purified soluble antigens for the induction of mucosal immune responses. Although the mechanisms by which liposomes promote the induction of responses to soluble antigens have not been Clearly shown, it has been suggested that these vesicles, when given orally, are taken up by M cells for delivery of antigen to underlying lymphoid cells in the Peyers patch which serves as an adjuvant for processing of antigen for secretory immune responses. This proposal will examine the characteristics of liposomes that are important in potentiating immune responses to orally administered S. mutans antigens (serotype c carbohydrate antigen and glucosyltransferase). In this regard, using transmission electron microscopy, in vitro experiments will be conducted to determine the physical characteristics of liposomes and antigen location in liposomes. Subsequent in vivo studies will assess the fate of the liposomal vesicles as they are taken up by M cells in an experimental rat model as well as optimum liposome/antigen characteristics for this uptake. Using an established gnotobiotic rat caries model, antigen/liposome preparations will be assessed for their effectiveness in inducing protective immune responses. Human oral immunization studies will also be continued in order to establish the applicability of this vaccine delivery system and to determine the properties of this vaccine important for the induction of mucosal responses. Human volunteers will ingest enteric coated capsules containing liposome/antigen preparations for seven days. Immune responses will be monitored by analysis of parotid saliva, tears and plasma for antigen specific antibody responses. Additionally, changes in levels of colonization of dental plaque with S. mutans will be determined. ELISPOT analysis will be done with peripheral blood lymphocytes to detect the migration of antigen specific B-cells to local secretory sites. In conclusion, the proposed studies are directed at defining a practical and yet effective oral liposome/S. mutans antigen delivery system for the induction of protective mucosal immune responses. Not only will these studies expand and extend our understanding of the mechanisms involved in the induction of mucosal immunity against S. mutans infection, but they will improve our understanding of ways to induce mucosal immunity against the multitude of other mucosal pathogens.